L4D

I just got this new PC, and I downloaded a non-steam version of L4D, the problem I have is not knowing what the problem is with my computer. So, my question is what can you see from the specs on http://www.newegg.com/Product/Product.aspx?Item=N82E16883107710 that would make it lag so badly, and what would be a cost efficient replacement for it to make it run nice and smooth. On another related note, the problem I have is control lagging, when i move the mouse, or anything else, while in-game, it takes it a short, but very noticeable amount of time to do that. This is a problem considering as how it often leads to death.